Column Leaching of Greek Low-Grade Limonitic Laterites

In this study, column leaching experiments were carried out to investigate the extraction of Ni and Co from low-grade limonitic laterites from Agios Ioannis mines in central Greece. Tests were carried out in laboratory Plexiglas columns using H2SO4 as leaching solution. Parameters determining the efficiency of the process, including acid concentration (0.5 M or 1.5 M) and addition of 20 or 30 g/L of sodium sulfite (Na2SO3) in the leaching solution, were also studied. Upflow transport of the leaching solution with the use of peristaltic pumps was implemented, while the pregnant leach solution (PLS) was recycled several times over the entire test duration. The concentration of Ni, Co, Fe, Ca, Al, Mg, and Mn in the PLS was determined by Atomic Absorption Spectroscopy (AAS). The ore and leaching residues were characterized by various techniques, including X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and differential scanning calorimetry and thermogravimetry (DSC/TG). Results indicated that Ni and Co extractions increased with higher H2SO4 concentration, reaching 60.2% and 59.0%, respectively, after 33 days with 1.5 M H2SO4. Additionally, adding 20 g/L Na2SO3 significantly enhanced extraction percentages (73.5% for Ni and 84.1% for Co). The selectivity improved with 1.5 M H2SO4 and 20 g/L Na2SO3, evidenced by the elemental ratios in the PLS.